\documentclass{standalone}
\usepackage{tikz}
\usepackage{ctex,siunitx}
\setCJKmainfont{Noto Serif CJK SC}
\usepackage{tkz-euclide}
\usepackage{amsmath}
\usepackage{wasysym}
\usepackage{circuitikz}
\usetikzlibrary{patterns, calc}
\usetikzlibrary {decorations.pathmorphing, decorations.pathreplacing, decorations.shapes,}
\ctikzset{bipoles/length=1cm}
\begin{document}
\small
\begin{circuitikz}[>=latex, scale=0.8,european]
  % \useasboundingbox(0.9,0)rectangle(5.1,5);
  \draw(0,0) to [battery2] (6,0) node [below]{$B$} to[cute open switch] (6,2) to[R=$R$] (0,2)node [above]{$A$}--(0,0) ;
  \node at (6,1)[right]{$K$};
  \node at (3,-.5)[below]{$\mathcal{E}\;  r$};
\end{circuitikz}
\end{document}